Heparin is sulfate-containing polysaccharide which on a large scale is isolated from intestinal mucus from swine or lung from cattle. The avarage molecular weight for standard bovine heparin is more than 9,000 and for standard porcine heparin more than 12,000. Traditionally the clinical use of heparin has been associated with its anticoagulant and antithrombotic properties (Jorpes. E. 1946, Heparin in Treatment of Thrombosis, 2nd Ed. Oxford Medical Publications). Heparin has also been found to accelerate coronary collateral development in dogs (Fujita, M. Mikuniya, A. Takahashi, M. Gaddis, R. Hartley, J. McKnown, D. and Franklin, D. 1987, Japanese Circulation Journal, 51, 395-402) and to improve collateral circulation in patients with effort angina (Fujita, M. Sasayama, S. Asanoi, H. Nakijama, H. Sakai, O. and Ohino, A. 1988, Circulation, 77, 1022-1029). Other effects such as the "anti-complementary power of heparin" recognized by Ecker, E. E. and Gross, P. (1929) in J. Infect. Dis. 44, 250-253 and the finding by Clowes, A. W. and Karnovsky, M. J. (1977) in Nature 265, 625-626 that heparin infusion following experimental injury suppressed the proliferation of smooth muscle cells, have not led to any widespread use of heparin for the treatment of diseases related to inflammation or to arteriosclerosis, which are associated with complement activation and smooth muscle cell proliferation respectively. The risk of haemorrhage is considered to be the main limitation for the clinical use of heparin in non-antithrombotic indications.
The patent application EP 287 477-A discloses heparin products with low molecular weight and this document gives a good review of prior art relating to oxidation of heparin by periodate and to low molecular weight heparins obtained in this manner. Reference is herein given to this document.
In EP 287 477, it was shown that, when heparin obtained from porcine intestinal mucosa was subjected to treatment with periodate at pH 5 followed by depolymerization by treatment with a strong base at a pH above 11 and then reduced by a reducing agent, a low molecular weight heparin was obtained which had 70% of its molecular weight distributed between 4800-9000 Da and a peak molecular weight of 5500-6000 Da as determined by HPLC. This low molecular heparin is used for regulation of the physiological system.
We have now found that the low molecular weight heparins (heparin fragments) corresponding to EP 287 477 did not significantly accelerate the coronary collateral development. However, unexpectedly. we have found that our novel heparin derivatives of a molecular weight equal to or larger than standard heparin which have an enhanced sulfur content, retain the valuable physiological properties of standard heparin such as the enhancement of coronary collateral development. In addition we have also shown a much smaller effect on the bleeding time for our novel heparin derivatives than for heparin itself. We have also shown a potent antithrombotic activity of our novel heparin derivatives at a dose in which the bleeding time is not prolonged. Thus our novel heparin derivatives are superior to the products claimed in EP 287 477 and will constitute useful drugs for treatment of ischemic heart disease such as angina and related vascular disorders, e.g. to prevent restenosis after percutaneous transluminal angioplasty (PTCA).
Patients suffering from ischemic heart disease generally show a narrowing of the arteries in the heart. Progressive narrowing of the lumen of coronary arteries gives rise to the symptoms of angina and finally often to a myocardial infarction (MI). Excessive uncontrolled growth of smooth muscle cells (SMC) constitutes a major contribution to the progressive narrowing of the coronary vessel. The final occlusion of a stenotic vessel, which precipitates the myocardial infarction, is most frequently caused by formation of a thrombus. The thrombus formation might be triggered by activation of the coagulation and complement systems which by themselves become activated by the sclerotic surface of the stenotic artery. As a natural defense mechanism to the reduced blood flow and thus reduced oxygen supply to these parts of the heart which are supplied by the stenotic blood vessels new routes of blood supply slowly develop in some patients, whereas in other patients hardly at all. These new routes of blood supply to an oxygen deficient (ischemic) area of the heart are called collaterals and the process of formation of new blood vessels is called angiogenesis. The new routes can be small or large vessels. Here they are collectively referred to as collaterals. It has been shown that heparin has a stimulatory effect on coronary collateral development and the process of angiogenesis as well as an inhibitory effect on SMC proliferation and a preventive effect on thrombus formation. However a major obstacle for a general use of heparin in ischemic heart disease is the risk for bleeding which is associated with therapy using standard heparin. The present invention describes novel heparin derivatives which enhance coronary collateral formation, inhibit SMC proliferation and maintain a low level of anticoagulant activity in blood without being hazardous with respect to bleeding thus being suitable for treatment in ischemic heart disease e.g. angina pectoris and related vascular disorders. An example of related vascular disorders is treatment of patients having had a percutaneous transluminal coronary angioplasty (PTCA) procedure to prevent restenosis.